The present invention relates to portable pumping devices capable of operating either as a suction pump or as a compressor. The invention is particularly applicable to the portable fluid pumping devices described in my prior U.S. Pat. No. 4,726,745, and is therefore described below with respect to this type of device.
My U.S. Pat. No. 4,726,745 discloses a portable pumping device particularly useful as a medical suction pump for drawing off waste fluids. The pumping device described in that patent is now in production, but one of its drawbacks is that it requires a rolling diaphragm between the piston and cylinder. Rolling diaphragms, however, degrade with time and deform under pressure to introduce "dead" piston travel which stretches the diaphragm without displacing air. Such pumps, therefore, require frequent replacement of the diaphragm.
In addition, pumps of this type are extremely noisy at the exhaust end when operating as a suction pump, and at the air-intake end when operated as a compressor. Furthermore, when such pumps are operated as a compressor, the air entering the pump or exiting from it has to be filtered, and providing an external filter is both costly and cumbersome.